Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with graphical user interface showing a new design.

The broken lines showing of text boxes, text, words, letters, symbols, icons, numbers, images, and lines are included for the purpose of illustrating portions of the article and form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with graphical user interface, as shown and described. 